Flotation separation of phosphate ores



United States Patent Ofiiice 3,164,549 Patented Jan. 5, 1965 This invention relates to the flotation separation of phosphate ores, and more particularly to the separation of phosphate ores through frothflotation.

In the present day commercial separationof phosphate ores, the practice is to employ a two-step process in which the phosphate material is first floated away from the silica and thereafter the flotation is reversed to float the silica away from the phosphate materiahthe phosphate concentrate being recovered in the underflow. In the first step of the process, fuel oil and tall oil are employed, and to this mixture is added caustic soda. In the second step, the phosphate is floated away from the silica by employing a cationic collector such as an amine or amines.

The aboige process is applicable to phosphate ores only and it is well understood that phosphate is afiected differently from other ores such as the metalic ores, so that a special art has developed in the field of phosphate separation.

I have discovered that the phosphate fraction can be effectively recovered in a single step process by employing with the fuel oil certain anionic, water-soluble and oilsoluble surfactants. The need for tall oil and caustic soda is eliminated, and the need for a second reverse flotation employing amines is made unnecessary.

A primary object, therefore, is to provide a new and simplified procedure for the recovery of the phosphate product with a consequent saving in time and expense. A further object is to provide a new process for the recovery of the phosphate fraction of phosphate ores by conditioning thesame in water suspension with fuel oil and certain anionic, water-soluble and oil-soluble surfactants, as set out hereinafter. Another object is to provide a further improved process in which waste scrub water is utilized to effect a reverse flotation separation, causing the silica to float away from thephosphate fraction. Other specific objects and advantages will appear as the specification proceeds.

In one embodiment of the invention, phosphate ore, after passing through the preliminary washing and screening operations to remove the clay constituents or slime and to recovera finely-divided material desired for treatment, say, the material between 14 or 35 mesh to 150 mesh, is in water suspension conditioned with fuel oil and a water-soluble and oil-soluble alkyl aryl sulfonic acid, polyalkyl aryl sulfonic acid, or the water-soluble salts of these acids, and flotation is accomplished in the usual manner by the admission of air to form bubbles which float the phosphate fraction. As a specific example, I have conditioned a water suspension of finely-divided phosphate ore with fuel oil and dodecyl benzene sulfonic acid and then subjected the reagentized ore to flotation separation in a conventional flotation cell to recover more than 98% of the P content of the ore in a single flotation procedure.

The fuel oil may be the usual fuel oil employed in phosphate flotation procedures, and it may be employed in the usual amounts.

The reagent employed with the fuel oil is an alkyl aryl sulfonic acid or polyalkyl aryl sulfonic acid. These reagents are anionic in nature and are water-soluble as well as oil-soluble. I may also use the salts of these compounds, particularly the sodium salts. While the alkyl chain length may vary, I prefer that at least one alltyl radical have a chain length of from 4 to 18 carbon atoms,

,ing as in the usual practice.

and recommend that the aliphatic hydrocarbon have from 6 to 13 carbon atoms. For the purpose of this description, the term alkyl is intended to include both saturated and unsaturated radicals. The aryl portion of the compound may be, for example, benzene, toluene, xylene, mesitylene, durene, biphenyl, or napthalene.

A reagent which has been shown to have great advantage in my process, is dodecyl benzene sulfonic acid. A compound of this character is commercially prepared by the sulfonation of dodecyl benzene, the dodecyl benzene being an alkylation product of benzene. Such compound is made and marketed commercially by Monsanto Chemical Company under the designation DDBSA.

In general, the DDBSA or other alkyl aryl sulfonic acid may be employed in an amount which is of the order of 0.1 lb. to 2 lbs. per ton of feed material and having a ratio to the amount of fuel oil of from 0.01:1 to 05:1. Amounts and proportions outside these ranges may be used, but on the lower side the maximum advantage may not be obtained and on the-higher side the added expense of the extra reagent may not be justified.

In this improved process, the fuel oil and the DDBSA or other alkyl aryl sulfonic acid are added to the phosphate feed material and mixed to bring the fuel oil and reagent into contact with all parts of the feed. The reagentized feed may be diluted with water to a concentration of 10-35% solids, and subjected to froth flotation in a standard flotation cell. It is not necessary to adjust the pH of the pulp since the natural pH is in this process entirely satisfactory. The natural pH of the pulp in the Florida operations is slightly below 7.0, usually about 6.5, and in substantially all situations the natural pH will be between 6 and 8. The process is operable, however, when the pH is lowered by addition of acid or raised by addition of caustic soda.

The phosphate concentrate is removed in the froth and the tailing or underflow material is rejected.

When the reagent is added in the form of a salt such as the sodium salt, the same procedure may be followed, suitably in the case with adjustment of pH to the acid side by addition of an acid such as sulfuric acid.

While it is possible to obtain a high yield of phosphate in the single step operation using the reagents just described, I have found that a still higher grade product may be prepared by combining with this operation a treatment of the concentrate with scrubber water. Scrubber water is normally a waste product from the wet process manufacture of phosphoric acid, or from processes for manufacture of superphosphate or triple superphosphate. It contains hydrofluosilicic acid and minor amounts of other ingredients.

The phosphate concentrate obtained by flotation separation using the DDBSA or other alkyl aryl sulfonic acid or salts thereof, may be treated by washing and dewater- Then the scrubber water is added to the concentrate, and the mixture subjected to froth flotation in a cell to remove the silica in the overhead froth fraction and to recover the phosphate in the underflow.

Instead of using the scrubber water as above explained, I may use hydrofluosilicic acid, sulfuric acid, or equivalents thereof. A function of this treatment is to deoil the previously reagentized mixture, and the fuel oil is recovered along with the silica in the froth. The fuel oil may then be separated from the silica fraction by gravity separation and reused in further flotation operations. An exceptionally high grade phosphate product is obtained by this procedure.

Example I 1 ton 16 +20 mesh 66.6 BPL phosphatic flotation feed was reagentized with 13.8 pounds of fuel oil and procedure.

1 ton of 20 +35 mesh 50.2 BPL phosphatic flotation feed was reagentizedwith 12.6 pounds of fuel oil and 0.26 pound of dodecyl benzene sulfonic acid. Subsequent single flotation of the reagentized flotation feed was effected in a Denver flotation cell. 73.3 BPL phosphatic concentrate constituting 98.2% of the P content of the flotation feed was recovered by this single flotation procedure.

Example III 1 ton of 35 +150 mesh 34.9 BPL phosphatic flotation feed was reagentized with 7 pounds of fuel oil and 0.52 pound of dodecyl benzene sulfonic acid. Subsequent single flotation of the reagentized flotation feed was effected in a Denver flotation cell. 73.2 BPL phosphatic concentrate constituting 83.7% of the P 0 content of the flotation feed was recovered by this single flotation Example IV I may repeat the procedure under substantially the same conditions as given in Examples I, II and III except that instead of using closely sized feed material, use feed material of approximately 14 +150 mesh.

Example V I followed the same general procedure as set forth in 5 Examples I, II and III, except that instead of using dodecyl benzene sulfonic acid I used the sulfonic acid .produced by the reaction of petrol AA with oleum which is a polyalkyl napthalene sulfonic acid. Results comparable to those set forth in Examples I, II and III were obtained.

Example.VI

67 BPL phosture to froth flotation separation. The scrubber water came from the process for making triple superphosphate by reacting phosphate rock and wet process phosphoric acid. It contained hydrofluosilicic acid and had a pH of approximately 1.5. An oily fraction containing silica was separated in the froth portion, and a phosphate fraction was recovered as the underflow. The phosphate product tested 75.6 BPL. I A

While in the foregoing specification I have set forth specific process steps in'considerable detail for the purpose of illustrating embodiments of my invention, it will be understood that such details may be varied widely by those skilled in the art without departing from the spirit and scope of my invention.

I claim:

1. In a process for the separation of phosphatic ores by froth flotation and for the recovery of phosphate values from the froth, the step of conditioning a water suspenpension of finely-divided phosphate ore with fuel oil and dodecyl benzene sulfonic acid.

2. In a process for the separation of phosphatic ores by froth flotation and the recovery of phosphate values from the froth, the step of conditioning a water suspension of finely-divided phosphate ore with fuel oil and a water-soluble salt of dodecyl benzene sulfonie acid.

3. In a process for the separation of phosphatic ores by froth flotation and the recovery of phosphate values from the froth, the step of conditioning a water suspension of finely-divided phosphate ore with fuel oil and a sodium salt of dodecyl benzene sulfonic acid.

References Cited in the file of this patent UNITED STATES PATENTS 1,765,308 Lutz June 17, 1930 2,230,565 Gaylor Feb. 4, 1941 2,373,688 Keck Apr. 17, 1945 2,433,258 Booth Dec. 23, 1947 2,442,455 Booth June 1, 1948 2,446,207 Bishop Aug. 3, 1948 2,547,148 Bates Apr. 3, 1951 2,698,088 Pryor Dec. 28, 1954 2,748,939 Hodges June 5, 1956 2,834,463 Vincent May 13, 1958 2,838,564 Norwood et a1 June 10, 1958 FOREIGN PATENTS 584,206 Australia Jan. 9, 1947 OTHER REFERENCES Industrial and Engineering Chemistry, Sperling, volume 40, number 5, May 1948, pages 890-897. 

1. IN A PROCESS FOR THE SEPARATION OF PHOSPHATIC ORES BY FROTH FLOTATION AND FOR THE RECOVERY OF PHOSPHATE VALUES FROM THE FROTH, THE STEP OF CONDITIONING A WATER SUSPENPENSION OF FINELY-DIVIDED PHOSPHATE ORE WITH FUEL OIL AND DODECYL BENZENE SULFONIC ACID. 